I'm not wholly opposed to the idea (it only adds a few extra characters to the status, so I don't see much of a problem--except for series with many editions, where it could get pretty crowded), but isn't it much easier to just check the "completely scanlated?" field?
I wouldn't say that adding chapter numbers would be a bad idea; rather, I think that it's simply much more advantageous to stick to volume numbers. The number of volumes is just more... "consistent" than the number of chapters, and is thus a more helpful detail. The number of chapters during serialization is not necessarily the same as in the tankobons. For example, volume 7 of Historie includes chapters 58-65 which are chapters 60-70 of the magazine serialization; not only is the numbering different, but 11 chapters were merged into just 8 chapters. You could probably reconcile this as:
If you're worried about which chapter is the last one - there's also the 'Completely Scanlated?' section. It it's set to 'Yes.', then the last release is usually the last chapter (unless there's more than one scanlator).
@chueisha: That's what the "completely scanlated" section is for. That and the status in country of origin are independent of each other.
I'm not sure I completely understand what you are saying... I'm saying that we can't exactly see what the last chapter is by looking at the scanlation status since the scanlation status may be ongoing while the country's status may be complete already. It's a reply to Gradonil_Ral's post.